Cam ring bearing for fuel delivery system

ABSTRACT

A bearing assembly is provided for a fuel delivery system that includes a pump ( 10 ) having a housing that rotatably receives a rotor ( 20 ) carrying vanes ( 26 ) thereon, a cam ring ( 70 ) received between the housing and rotor ( 20 ), and a support member of yoke ( 50 ) encompassing the cam ring ( 70 ) to selectively vary fuel flow. The bearing assembly ( 80 ) is a journal bearing between the yoke ( 50 ) and the cam ring ( 70 ) and includes an annular surface having a central opening therethrough. The annular surface includes a first, high pressure pad ( 102 ) and a second, low pressure pad ( 104 ) substantially diametrically opposite the first pad and separated by first and second lands ( 106, 108 ). The circumferential extent of the first pad ( 102 ) is at least as great as an inner diameter of the cam ring ( 70 ). Circumferential ends of the second pad ( 104 ) are wider than circumferential ends of the first pad. The first and second pads ( 102, 104 ) are formed by circumferentially extending grooves that extend an entire width of the bearing so that the cam ring moves between the first and second pads, and thereby varies a clearance between the lands ( 106, 108 ) and the cam ring ( 70 ).

BACKGROUND OF THE INVENTION

The present invention relates to a bearing arrangement, and moreparticularly to a bearing arrangement used to support a cam ring withina support member or yoke in a hydrostatic and hydrodynamic configurationfor use in fuel pumps, metering, and control for jet engines.

PCT/US02/09298, filed Mar. 27, 2002, the details of which areincorporated herein by reference, relates to a fuel delivery systemhaving increased efficiency and reliability over known fuel pumparrangements. Particularly, a pump of a fuel delivery system includes ahousing having a chamber with an inlet and outlet in fluid communicationwith the pump chamber. A rotor is received in the pump chamber, and acam member surrounds the rotor and is freely rotatable relative to thehousing and the rotor. A journal bearing is formed between the cam ringand a support sleeve or yoke that is precluded from rotation within thehousing.

The bearing arrangement must be responsive to hydrostatic andhydrodynamic forces imposed thereon by the internal components of thepumping mechanism. Known bearing arrangements require improvement toproperly support the cam ring in a combined hydrostatic and hydrodynamicarrangement. Accordingly, a need exists for a new bearing assembly.

SUMMARY OF THE INVENTION

An improved bearing assembly is provided for a fuel delivery system thatincludes a housing receiving a rotor within a rotatable cam ring, wherethe cam ring is freely rotatable relative to the housing and the rotor.The bearing assembly includes an annular surface having a centralopening dimensioned to receive the associated cam ring.

The annular surface includes a first, high pressure pad and a second lowpressure pad spaced by first and second lands.

The circumferential extension of the first pad is at least as great asan inner diameter of the cam ring.

Circumferential ends of the second pad are preferably wider than thecircumferential ends of the first pad.

A differential pressure is established across the pump chamber and thecam ring is capable of movement between the high and low pressure padsin response to pressure variations. Clearance between the land and thecam ring selectively alters the flow of fluid through the bearing tomaintain a pressure. This creates a relatively stiff bearing mountwithout deflection concerns.

A primary advantage of the invention resides in an improved bearinginterface between a rotating cam ring and stationary (non-rotatable),but moveable yoke.

Another advantage of the invention resides in the structure beingcapable of providing hydrostatic bearing capabilities, as well ashydrodynamic bearing capabilities.

Still other benefits and advantages of the invention will becomeapparent to those skilled in the art upon a reading and understanding ofthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a preferred embodiment of thefluid pump.

FIG. 2 is a cross-sectional view through the assembled pump of FIG. 1.

FIG. 3 is a longitudinal cross-sectional view through the assembledpump.

FIG. 4 is a cross-sectional view similar to FIG. 2 illustrating avariable displacement pump with the support ring located in a secondposition.

FIG. 5 is an enlarged cross-sectional view of the pump.

FIG. 6 is an exploded perspective view of the bearing assembly.

DETAILED DESCRIPTION OF THE INVENTION

As shown in the Figures, a pump assembly 10 includes a housing 12 havinga pump chamber 14 defined therein. Rotatably received in the chamber isa rotor 20 secured to a shaft 22 for rotating the rotor within thechamber. Peripherally or circumferentially spaced about the rotor are aseries of radially extending grooves 24 that operatively receive bladesor vanes 26 having outer radial tips that extend from the periphery ofthe rotor. The vanes may vary in number, for example, nine (9) vanes areshown in the embodiment of FIG. 2, although a different number of vanescan be used without departing from the scope and intent of the presentinvention. As is perhaps best illustrated in FIG. 2, the rotational axisof the shaft 22 and rotor 20 is referenced by numeral 30. Selected vanes(right-hand vanes shown in FIG. 2) do not extend outwardly from theperiphery of the rotor to as great an extent as the remaining vanes(left-hand vanes in FIG. 2) as the rotor rotates within the housingchamber. Pumping chambers are defined between each of the vanes as thevanes rotate in the pump chamber with the rotor and provide positivedisplacement of the fluid.

With continued reference to FIG. 2, a spacer ring 40 is rigidly securedin the housing and received around the rotor at a location spacedadjacent the inner wall of the housing chamber. The spacer ring has aflat or planar cam rolling surface 42 and receives an anti-rotation pin44. The pin pivotally receives a cam sleeve 50 that is non-rotatablyreceived around the rotor. First and second lobes or actuating surfaces52, 54 are provided on the sleeve, typically at a location opposite theanti-rotation pin. The lobes cooperate with first and second actuatorassemblies 56, 58 to define means for altering a position of the camsleeve 50. The altering means selectively alter the stroke ordisplacement of the pump in a manner well known in the art. For example,each actuator assembly includes a piston 60, biasing means such asspring 62, and a closure member 64 so that in response to pressureapplied to a rear face of the pistons, actuating lobes of the cam sleeveare selectively moved. This selective actuation results in rollingmovement of the cam sleeve along a generally planar or flat surface 66located along an inner surface of the spacer ring adjacent on the pin44. It is desirable that the cam sleeve undergo a linear translation ofthe centerpoint, rather than arcuate movement, to limit pressurepulsations that may otherwise arise in seal zones of the assembly. Inthis manner, the center of the cam sleeve is selectively offset from therotational axis 30 of the shaft and rotor when one of the actuatorassemblies is actuated and moves the cam sleeve (FIG. 2). Other detailsof the cam sleeve, actuating surface, and actuating assemblies aregenerally well known to those skilled in the art so that furtherdiscussion herein is deemed unnecessary.

Received within the cam sleeve is a rotating cam member or ring 70having a smooth, inner peripheral wall 72 that is contacted by the outertips of the individual vanes 26 extending from the rotor. An outer,smooth peripheral wall 74 of the cam ring is configured for freerotation within the cam sleeve 50. More particularly, a journal bearing80 supports the rotating cam ring 70 within the sleeve. The journalbearing is filled with the pump fluid, here jet fuel, and defines ahydrostatic or hydrodynamic, or a hybrid hydrostatic/hydrodynamicbearing. The frictional forces developed between the outer tips of thevanes and the rotating cam ring 70 result in a cam ring that rotates atapproximately the same speed as the rotor, although the cam ring is freeto rotate relative to the rotor since there is no structural componentinterlocking the cam ring for rotation with the rotor. It will beappreciated that the ring rotates slightly less than the speed of therotor, or even slightly greater than the speed of the rotor, but due tothe support/operation in the fluid film bearing, the cam ring possessesa much lower magnitude viscous drag. The low viscous drag of the camring substitutes for the high mechanical losses exhibited by known vanepumps that result from the vane frictional losses contacting thesurrounding stationary ring. The drag forces resulting from contact ofthe vanes with the cam ring are converted directly into mechanicallosses that reduce the pumps overall efficiency. The cam ring issupported solely by the journal bearing 80 within the cam sleeve. Thejournal bearing is a continuous passage. That is, there is nointerconnecting structural component such as roller bearings, pins, orthe like that would adversely impact on the benefits obtained by the lowviscous drag of the cam ring. For example, flooded ball bearings wouldnot exhibit the improved efficiencies offered by the journal bearing,particularly a journal bearing that advantageously uses the pump fluidas the fluid bearing.

In prior applications these mechanical drag losses can far exceed themechanical power to pump the fluid in many operating regimes of the jetengine fuel pump. As a result, there was a required use of materialshaving higher durability and wear resistance because of the highvelocity and load factors in these vane pumps. The material weight andmanufacturing costs were substantially greater, and the materials alsosuffer from high brittleness. The turning speed of those pumps was alsolimited due to the high vane sliding velocities relative to the camring. Even when using special materials such as tungsten carbide, highspeed pump operation, e.g., over 12,000 RPM, was extremely difficult.

These mechanical losses resulting from friction between the vane and camring are replaced in the present invention with much lower magnitudeviscous drag losses. This results from the ability of the cam ring torotate with the rotor vanes. A relatively low sliding velocity betweenthe cam ring and vanes results, and allows the manufacturer to use lessexpensive, less brittle materials in the pump. This provides forincreased reliability and permits the pump to be operated at much higherspeeds without the concern for exceeding tip velocity limits. In turn,higher operating speeds result in smaller displacements required forachieving a given flow. In other words, a smaller, more compact pump canprovide similar flow results as a prior larger pump. The pump will alsohave an extended range of application for various vane pump mechanisms.

FIG. 3 more particularly illustrates inlet and outlet porting about therotor for providing an inlet and outlet to the pump chamber. First andsecond plates 90, 92 have openings 94, 96, respectively. Energy isimparted to the fluid by the rotating vanes. Jet fuel, for example, ispumped to a desired downstream use at an elevated pressure.

As shown in FIG. 4, neither of the actuating assemblies is pressurizedso that the cam sleeve is not pivoted to vary the stroke of the vanepump. That is, this no flow position of FIG. 4 can be compared to FIG. 2where the cam sleeve 50 is pivoted about the pin 44 so that a closeclearance is defined between the cam sleeve and the spacer ring 40 alongthe left-hand quadrants of the pump as illustrated in the Figure. Thisprovides for variable displacement capabilities in a manner achieved byaltering the position of the cam sleeve.

In the preferred arrangement, the vanes are still manufactured from adurable, hard material such as tungsten carbide. The cam ring and sideplates, though, are alternately formed of a low cost, durable materialsuch as steel to reduce the weight and manufacturing costs, and allowgreater reliability. Of course, it will be realized that if desired, allof the components can still be formed of more expensive durablematerials such as tungsten carbide and still achieve substantialefficiency benefits over prior arrangements. By using the jet fuel asthe fluid that forms the journal bearing, the benefits of tungstencarbide for selected components and steel for other components of thepump assembly are used to advantage. This is to be contrasted with usingoil or similar hydraulic fluids as the journal bearing fluid where itwould be necessary for all of the jet fuel components to be formed fromsteel, thus eliminating the opportunity to obtain the benefits offeredby using tungsten carbide.

As illustrated in greater particularity in FIGS. 5 and 6, the journalbearing assembly defined by the interface between the cam sleeve or yoke50 and the cam ring 70 is shown in greater detail. Particularly, theinner surface 100 of the support sleeve or yoke is a non-constantdiameter to define discrete portions of the bearing arrangement.Specifically, a first or large diameter portion 102 defines a first,high pressure pad and a diametrically opposite, second or low pressurepad 104. For ease of description, and as will be appreciated from FIG.5, the high pressure pad portion 102 extends from approximately 4o'clock to 8 o'clock while the low pressure pad extends fromapproximately 10 o'clock to 2 o'clock. Separating the high pressure padfrom the low pressure pad are first and second seal lands 106, 108. Thefirst seal land 106, therefore extends from approximately 2 o'clock to 4o'clock, while the second seal land 108 extends from approximately 8o'clock to 10 o'clock.

The bearing arrangement defines a combination hydrostatic andhydrodynamic configuration. The hydrostatic portion of the bearing isthe two pad arrangement defined by the high pressure and low pressurepads 102, 104, respectively. The high pressure pad is a groove cutthrough the full width or extent of the yoke, i.e., from a front face 50a to a rear face 50 b, as will be more clearly appreciated from a reviewof FIG. 6. Likewise, the low pressure pad is also a groove through thefull width of the yoke. The high pressure pad is capable of supportingthe forces generated by the internal components of the pumpingmechanism. Between the two pads, in the yoke, are the seal lands 106,108 that create a hydrodynamic effect that enables smooth start-up andcenters the cam ring within the bearing during operation.

The high pressure pad geometry is determined so that the force generatedby the fluid pressure is slightly greater than the forces generated bythe internal pumping elements. The circumferential extent of the pad102, i.e., from 4 o'clock to 8 o'clock, is determined by the radialthickness of the cam ring. It is preferred that the edges 102 a, 102 bof the high pressure pad are located outside the inside diameter 72 ofthe cam ring (see FIG. 5). The seals and the sides of the high pressuregroove, that is along the faces 50 a, 50 b of the yoke, are created bythe port plates 90, 92 (FIG. 3) which clamp across the pumping element.High pressure fluid (jet fuel) is fed into the pad through openings 120shown in FIG. 6 and the flow to the interface between the yoke and thecam ring is restricted through orifices 122 (only one of which is seenin the view of FIG. 6). As will be appreciated, the high pressureorifices 122 communicate with respective openings or holes 120 in thisregion of the bearing assembly.

The geometry of the low pressure pad 104 is determined by settingcircumferential edges 104 a, 104 b slightly wider than thecircumferential edges of the high pressure pad, i.e., slightly widerthan 102 a, 102 b, respectively. Venting from the high pressure pad tothe low pressure pad must be provided in this pad such that highpressure does not build. This is provided through openings 124, one ofwhich is illustrated in FIG. 6. As will be apparent, openings 124 have asubstantially larger diameter than openings 122. Therefore, adifferential pressure is established across the yoke to react the forceswithin the pumping element.

The high and low pressure pads 102, 104 are cut completely through thebearing, i.e., they extend completely from face 50 a to 50 b, to allowthe cam ring to move in the vertical direction as depicted in FIG. 5.The movement in the vertical direction allows for radial deflection ofthe yoke in the horizontal direction, thus increasing the clearancebetween the lands and the cam ring. When the clearance increases, theflow through the bearing must increase to maintain the pressure in thehigh pressure pad, or the clearance must be reduced. The orifices 122 onthe high pressure pad side restrict the flow and thus the cam ring movesvertically forward decreasing the clearance to re-establish anequilibrium force condition. This creates a relatively stiff bearingwithout the concerns of deflection.

The entire bearing, yoke 50 and cam ring 70 is free to roll within thepumping mechanism as described above. As shown in FIG. 5, the bearingrolls leftwardly or rightwardly along the generally planar surface 42provided in the spacer ring 40. This rolling on the surface 42 acts toprovide a linear translation of the cam ring. Linear cam ringtranslation is critical to minimizing fluid pump pressure pulsationduring operation. Sliding and rotation of the yoke are prevented by theanti-rotation disks 44 inserted on each side of the yoke. As will beapparent from FIG. 6, these anti-rotation disks 44 are dimensioned forreceipt in arcuate recesses or cutouts 130, only one of which isillustrated in FIG. 6, although it will be appreciated that a similarcutout recess is provided on the rear surface 50 b of the yoke. Thus,these anti-rotation disks 44 do not pass completely through the yoke, orcorresponding recesses provided in the spacer ring, and thereby allowthe forces in yoke to be transmitted to the housing structure throughthe spacer ring.

It will also be appreciated that in the preferred embodiment of the yoke50, an undercut 140 is provided on the first and second surfaces 50 a,50 b. The undercut 140 is provided at the outer radial perimeter ofthese faces. Moreover, the undercut extends circumferentially aroundsubstantially the entire yoke, i.e., from approximately 6:30 in aclockwise direction to approximately 5:30. The undercut facilitatescontrol of pressure on the face of the yoke and accurately predicts orcontrols the pressure of the overall pump arrangement.

The invention has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations in so far as they come within thescope of the appended claims or the equivalents thereof.

1. In a fuel delivery system having a housing that rotatably receives arotor carrying vanes thereon and received within a rotatable cam ringlocated between the housing and the rotor and freely rotatable relativeto each of the housing and rotor, the bearing assembly comprising: ahydrostatic and hydrodynamic bearing member including an annular surfacehaving a central opening dimensioned to receive the associated cam ringtherein, the annular surface including a first, high pressure pad and asecond, low pressure pad substantially diametrically opposite the firstpad, and first and second lands separating the first and second pads forcentering the associated cam ring during operation.
 2. The bearingassembly of claim 1 wherein the circumferential extent of the first padis at least as great as an inner diameter of the associated cam ring. 3.The bearing assembly of claim 2 wherein circumferential ends of thesecond pad are wider than circumferential ends of the first pad.
 4. Thebearing assembly of claim 1 wherein the first and second pads are formedby circumferentially extending grooves that extend an entire width ofthe bearing.
 5. The bearing assembly of claim 1 further comprising meansfor preventing rotation of the bearing member.
 6. The bearing assemblyof claim 5 wherein the preventing means further prevents relativesliding between the cam ring and the bearing member.
 7. A bearingassembly for an associated fuel delivery system having a housing thatrotatably receives a rotor carrying vanes thereon, and a cam ringrotatably received between the housing and rotor, and a yokeencompassing the cam ring and selectively movable relative to thehousing to vary fuel flow from the system, the bearing assemblycomprising: a bearing member including an annular surface having acentral opening therethrough, the annular surface including a first,high pressure pad and a second, low pressure pad substantiallydiametrically opposite the first pad and separated by first and secondlands.
 8. The bearing assembly of claim 7 wherein the circumferentialextent of the first pad is at least as great as an associated innerdiameter of the associated cam ring.
 9. The bearing assembly of claim 8wherein circumferential ends of the second pad are wider thancircumferential ends of the first pad.
 10. The bearing assembly of claim7 wherein the first and second pads are formed by circumferentiallyextending grooves that extend an entire width of the bearing.
 11. Thebearing assembly of claim 7 further comprising means for preventingrotation of the bearing member.
 12. The bearing assembly of claim 1 1wherein the preventing means further prevents relative sliding betweenthe cam ring and the bearing member.
 13. The bearing assembly of claim 7further comprising a vent passage extending through the bearing andcommunicating with the second, low pressure pad to prevent high pressurefrom building.
 14. The bearing assembly of claim 13 wherein the ventpassage has a cross-sectional area greater than high pressure feedorifices whereby a pressure differential is established across the yoke.15. The bearing assembly of claim 14 wherein the cam ring moves betweenthe first and second pads, and thereby varies a clearance between thelands and the cam ring.
 16. The bearing assembly of claim 7 wherein thebearing assembly, comprised of the yoke and cam ring, is adapted forrolling movement relative to the housing whereby the cam ring undergoesselective linear translation.
 17. The bearing assembly of claim 7wherein the cam ring is adapted for linear translation relative to thehousing to minimize pressure pulsations during operation of the fueldelivery system.